In order to combine the imaging methods of magnetic resonance tomography (MR) and positron emission tomography (PET) in one machine, both the MR RF transmit-receive system and the PET detectors must be arranged inside the primary magnet and the MR gradient coil. However, arranging the RF system inside the PET ring presents the crucial disadvantage that the support structures and the cladding tube of the internally lying transmit and receive coils reduce the sensitivity of the PET detectors. A tube made of epoxy resins reinforced with glass fibers, or similar encapsulation materials which strongly attenuate the PET radiation owing to their high material density, is generally used as a support structure for the RF transmit antenna and at the same time sometimes also serves as cladding.